A Vertical Cavity Surface Emitting Laser (VCSEL) is a very attractive source for many applications. For instance, VCSELs typically generate a laser beam having a cross-section that is well defined, relatively narrow, and substantially symmetrical with respect to the transmission axis. Additionally, VCSELs are relatively easy to manufacture and standard semiconductor tooling and processes may be used in the manufacturing of the devices. Because of their generally vertical configuration, numerous VCSEL devices may be formed on a single wafer.
Although a single wafer may accommodate a large number of devices, the number of commercial-quality VCSELs that can be produced is typically much smaller because the fabrication yield is typically low. One of the reasons for the relatively low yield is that typically there are a number of uncontrolled factors in the fabrication process that often results in whole wafers being discarded because they fail to meet reliability screening criteria. Another reason is that even if the reliability criteria are met, the performance of individual devices may not meet requirements.
Both of these yield factors stem from various conventional techniques that are used to control the dimensions of the generally columnar-shaped volume of semiconductor material that forms the laser cavity. In the relevant art, distinct process techniques are used to define the dimensions of the column-shaped laser cavity of conventional VCSELs. According to one technique, the active area and top and bottom mirrors, consisting of stack layers of AlGaAs with alternating indices of refraction, are formed to define the laser cavity portion. Then, a thicker layer of relatively high aluminum content AlGaAs at the bottom of the stack is oxidized to form a doughnut-like layer of oxide that defines the laser beam profile. Generally, the controlling of the oxidation of the aluminum to achieve a required beam diameter and produce an oxide layer that does not degrade during the operational life of the VCSEL is difficult and often results in low yields.